Dr. Daniel Raible and Dr. Aaron Swank work on the pointing, acquisition and tracking rig in the iROC test bed. This system utilizes star trackers to determine where iROC is in space, in order to point the communications laser to the ground terminal on earth to complete the link. Image Credit: NASA. For a larger version of this image please go here.

Back in the early history of transatlantic shipping, sea captains used sextants to point to the stars in order to navigate earthly destinations. Today, scientists at NASA's Glenn Research Center are developing advanced technologies using the same celestial navigation concepts, but this time to find Earth from the sea of deep space.

The Integrated Radio and Optical Communications project, called iROC, is an effort to improve the speed of data transmission to investigators on Earth. The goal is to develop communications hardware to orbit Mars and act as a relay station from all operating spacecraft, probes and rovers to transmit data back to Earth in a faster, more efficient way.

After data is received, iROC will use optical lasers to beam the information to one of three observatory telescopes around the world. And while the beam will expand as it travels to something as wide as the American Southwest, the challenge of receiving the transmission is quite daunting when Earth is the size of a pinhead from out in deep space.

"There is no GPS in deep space," says Dan Raible, co-principle investigator of iROC. "So in order to find Earth, you first have to know where you are, and that takes celestial navigation. Just like those sailors from the past knew about the North Star, we will use the same beacons in the sky to guide us."

iROC scientists are developing a pointing and tracking system to test in the laboratories at Glenn. Raible and his team are using a device you often see in planetariums. A large spherical projector beams stars onto a parabolic screen. iROC will use two sets of cameras to find two completely different locations in the sky. This will significantly reduce the chance of error.

An algorithm, which is the brain of the pointing and tracking system, will take both images, process them using an index of constellations and give an exact placement of the spacecraft.

"Just like we need two eyes to give us our depth perception, our system needs two views of the sky to give us precise positional information," explains Raible. "Since we know the orbital trajectory of all the planets to a fine resolution, once we know our location, iROC will know where to point the laser beam and it should hit the target back on Earth."

Once iROC investigators develop the pointing and tracking system, they face other challenges. When you are pointing a laser at a very small target, you can't have the beam moving around. But many systems aboard spacecraft create a certain amount of vibration. "If you are trying to keep the ground station in the center of the beam, but vibration is making it dance all over the place, then you are not transmitting data," says Raible. Damping vibration will be critical to the overall mission of iROC.

Solving these challenges will lead iROC scientists to accomplish their most important mission-- creating a communications network in deep space to beam data to scientists in a much faster way.

"We have spacecraft operating out there since the Apollo era and others launched last year like the Mars Curiosity Rover," says Raible. "But they all talk different languages and at different frequencies. Most of them do not talk to each other and beam directly to satellite dishes on Earth." The problem is that all this data from different sources can jam up the communications highway, slowing down science.

iROC seeks to create inter-operability between all these assets in space. For example, if Voyager 1, poised at the edge of the solar system, could talk to a relay station close to Mars, the network could beam signals more often sending more information in the 16 hours required to reach Earth.

"We want to get some new technology out there that talks to new vehicles as well as some of our heritage hardware," explains Raible. "We need to un-constrain the science of deep space missions by fixing the communications bottleneck."

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